Wafer inspection systems help semiconductor manufacturers increase and maintain integrated circuit (IC) chip yields. The IC industry employs inspection systems to detect defects that occur during the manufacturing process. Their main purpose is to monitor whether the process is under control. If the process is outside the scope of established norms, the system should indicate the problem and/or the source of the problem, which a manager of the IC fabrication process can fix. Some important inspection system characteristics are defect detection sensitivity and wafer throughput. Sensitivity and throughput are coupled such that greater sensitivity usually means lower throughput. There are both physical and economic reasons for this relationship.
The relative value of sensitivity and throughput depends on the function of the inspection system. There are three general functional requirements for these systems: first, detecting and classifying defects in process development, second, in monitoring a process line, and third, in monitoring a station. In process development one may tolerate low throughput in order to capture smaller defects and a greater range of defect types. However, in monitoring a production line or a station, cost-of-ownership, and thus throughput, becomes relatively more important. In this case, of course, the sensitivity must be adequate to capture the yield-limiting defects.
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor fabricator.
Thus, inspection systems are evolving from stand-alone “tools” that just found defects to a part of a more complete solution where detecting defects, classifying them, analyzing these results and recommending corrective action are their functions.
Existing systems and methods have been used for automatic defect inspection of semiconductor wafers. However, the inspection parameters of prior art systems and methods are rather limited in a high-throughput environment. For example, parameters such as coated film thickness or the process uniformity across the wafer are time-consuming and computationally expensive.
Present systems capture grayscale images of a semiconductor wafer under all possible combinations of red, green, and blue LED illumination. The grayscale images are currently used for automatic defect detection on semiconductor wafers, or to detect wafer-to-wafer process variation (G-view).